The present invention relates to a method for manufacturing a perpendicular magnetic recording medium. In particular, the invention relates to a method for forming a recording layer of a perpendicular magnetic recording medium.
Recently, due to demands for higher recording densities, magnetic recording media, in particular, magnetic disks for magnetic hard disk drives (HDDs) are showing rapid improvement in coercivity. CoCrPt-based ferromagnetic alloys, which are conventionally used to form magnetic layers on magnetic disks, have reached the limit of coercivity and become difficult to meet the recent demand for higher coercivity. In addition, the conventional longitudinal recording method involves the problem of thermal stability, creating a demand for better thermal stability characteristics. Thermal stability is a phenomenon which causes a signal, recorded on a magnetic recording medium, to begin decaying after a certain period. Finally, the recorded signal decays down to the noise level of the medium, making it impossible to retrieve the recorded signal. This is a result of making smaller magnetic grains in order to secure high S/N for high recording densities these days. Accordingly, replacing longitudinal magnetic recording by perpendicular magnetic recording is being considered in order to solve these problems.
In a high recording density area, perpendicular magnetic recording is highlighted as a method capable of attaining sufficiently high S/N ratio while securing good thermal stability. A perpendicular magnetic recording medium includes: a perpendicular magnetic recording layer composed of a perpendicular magnetization film to record an information signal; a soft magnetic under layer to raise the information signal read/write efficiency; and an intermediate layer lying between the perpendicular magnetic recording layer and the soft magnetic under layer to improve the crystalline structure of the perpendicular magnetic recording layer and control the crystal grain size. It is essential that a perpendicular magnetic recording layer with good magnetic properties can be formed stably. Therefore, studies of granular magnetic films are in progress. A granular magnetic film is a recording layer composed of a CoCrPt-based alloy having such an insulator as SiO2 added. To form a perpendicular magnetic recording layer, RF (Radio Frequency) sputtering is mainly used. Patent Document 1 (Japanese Patent Laid-Open No. 2003-323709) discloses a sputtering method which uses a direct current pulsed voltage.